As tempting as it may be, letting go of all measures once you’re fully vaccinated doesn’t seem like a good idea. The Delta variant of the coronavirus is still widely circulated in the Netherlands, and fully vaccinated people can still get the virus and pass it on to others. This turns out to be happening more often than expected. Nine percent of all people who tested positive in the past few weeks have been fully vaccinated, RIVM reported on Wednesday, and 14 percent partially vaccinated. But more than three quarters, still the vast majority, have not been vaccinated.
It is no surprise that some of the vaccinated people can still get infected: none of the vaccines protect 100 percent against the virus. The mRNA vaccines from Pfizer and Moderna protected against disease by the original virus variant around 94 percent, the vector vaccines from Janssen and AstraZeneca around 70 percent. But the Delta variant does nibble about 6 to 8 percent of that, according to the latest calculations from Public Health England that Wednesday in the New England Journal of Medicine appeared.
Delta therefore breaks through the protection of the vaccination a little more easily. This is probably because someone who is infected with this variant already on the first day of virus production excretes more than a thousand times more virus particles than someone after an infection with the original variant, as shown in a Chinese study. That also makes the variant twice more contagious than the original variant. Perhaps the amount of antibodies in some vaccinees is not sufficient against such a high dose of the corona virus.
The Delta variant nibbles off 6 to 8 percent of the protection
This can be further enhanced because the antibodies may recognize the new variant slightly less well. Those of AstraZeneca-vaccinated people in India stick eight times less well to the protrusions of the Delta variant, British researchers reported in a preprint.
Still a lot unsure
But the protection against the Delta variant remains better in the studies than, for example, that against the Beta variant, which was first discovered in South Africa, according to vaccinologist Cécile van Els of Utrecht University and the RIVM. A full vaccination with Pfizer or AstraZeneca protects at least 92 percent against serious illness and hospitalization for the Delta variant.
However, there is still a lot of uncertainty. Not only about the extent to which the immune system that is generated protects, but also about how long it lasts. The latest data from Israel suggests that protection in the elderly may become more fragile over time. Monday night reported the Israeli Ministry of Health that an initial analysis shows that among the Israelis who were vaccinated first, protection against serious illness has fallen by 60 percent. The first to get a shot were people over 65, so this may indicate that the immune system in older people declines over time after vaccination, a well-known phenomenon. Israel is now considering giving the elderly a third shot, they are already doing that to people with a weakened immune system.
Uncertainty also reared its head on Wednesday about the protection of Janssen’s vaccine. In laboratory tests, the antibodies in the blood of people who received the Janssen vaccine recognize the characteristic protrusion of the Delta variant about six times worse than the antibodies of Pfizer and Moderna recipients. That’s what American researchers wrote Monday in a preprint. But that is no reason to panic, emphasizes immunologist Marjolein van Egmond of the Amsterdam UMC. “Laboratory tests with artificial viruses partly ignore the real-world situation. The Americans only looked at one part of the immune system.” In practice, there is also defense via specialized cells such as T cells. It is after vaccination with Janssen to be measured for at least eight months. “The real question is: do people who have received the Janssen vaccine get sick from Delta? We don’t have that data yet,” says Van Egmond.
Own research by Janssen
However, there is data from which the answer can be derived. “In a study by Janssen themselves, they also saw that there were fewer neutralizing antibodies against the Delta variant than against the original. But also that that amount is comparable to that against the Beta variant. Janssen has shown in a large study in South Africa that their vaccine protects 85 percent against serious illness, and complete protection against hospitalization and death due to the beta variant. That suggests that that protection will also be there against Delta,” says Van Egmond.
And also in Qatar turned out a vaccination with Moderna continues to protect against illness, hospitalization and death by both Alpha (the ‘British’ variant) and Beta.
This is in line with other findings from everyday practice: In the UK and the US, the vast majority of people who end up in hospital with Covid-19 are not vaccinated. “There are always a few people who are vaccinated and still end up in the hospital. But so far, the vaccines protect extremely well against severe Covid-19 and hospitalization,” said Van Egmond.
Still, there are already voices calling for a second shot after Janssen, or perhaps even a third shot after one of the other vaccines – research is already being done. That could strengthen the defenses. People who had already had Covid-19 before they received two shots of Pfizer or Moderna, and thus trained their defenses three times, so to speak, have broader defenses that better recognized the different virus variants, shows a preliminary study by researchers from the Yale University see that appeared on a preprint server this week.
“Immunologically, you expect that the immune system will improve, but we don’t know yet whether it is necessary. We could choose to do it just to be on the safe side. But studies into protection in daily practice are underway.”
A version of this article also appeared in NRC in the morning of July 22, 2021